When runners discuss running, we often talk about how fast we can do it. If you’re someone who runs races regularly, chances are you have your PR memorized and are always working to beat it.

Training plans call for a combo of speed runs and longer, slower runs to prep for distance races, from 5Ks all the way up to marathons. And while it might be tempting to add some urgency to every run you go on (the end goal is to be faster, right?), if you really want to shave seconds or minutes off your finish time, you need to run slowly.

Here’s why long, slow runs should be an essential part of every runner’s routine.

First, let’s establish what "slow" means.

"Slow" is a relative term. For the most part, a slow run should have you chugging along steadily at a low to moderate intensity level. If you were to categorize your exertion, it would fall at about a 6 on a scale of 1 to 10, Andrew Kalley, founder of Kalley Fitness and a NYC-based triathlon coach and personal trainer, tells SELF.

Kalley notes that your heart rate should stay below 145 beats per minute, ideally right around 135. If you don’t use a heart-rate monitor and want to just check your pulse, that’s a little over two beats per second. At the end of the day, if you focus on maintaining a conversational pace (you could chat with a running buddy without getting too winded), you’ll achieve ideal slowness.

Running slowly is the best way to build endurance, which you need to run long distances.

If you’re running a long-distance race, your body needs to be able to make it through. The more time you spend up and running, the better your body adapts to, gets accustomed to, and can endure the activity.

The slower you go, the greater percentage of your fuel comes from fat—and that’s beneficial when you’re training for an endurance race. "You want to prioritize fat as the main source of energy to sustain longer bouts of training," Milton adds. Fat takes longer to break down and is therefore a longer-lasting source of fuel than glycogen (carbs that our bodies have stored for later energy use), which is what our bodies turn to in short, intense bouts of exercise.

Slow runs also ease your body into the stresses of running so that you don’t end up hurting yourself.

“Running is one discipline that is very hard on your body; there’s a lot of stress going to your joints, ligaments, muscles, everything,” Katie Bottini, a NASM-certified physical trainer and running and triathlon coach, tells SELF.

Incorporating slow runs, whether you’re a beginner or seasoned racer, is a great way to prevent injuries. “You’re getting your body used to that repetitive stress,” Bottini explains, “by increasing those miles but doing it slowly so that you’re not increasing both volume and intensity all at once.”

It’s safer to build this foundation—and get your body used to the pounding motion—in a low-intensity environment. Then, when you start to increase speed incrementally, nothing will come as a total shock to your joints and muscles. Your body will be ready to handle what’s thrown its way.

Spending time on running slowly helps you avoid overtraining, so you can increase your speed safely and efficiently.

Going full speed ahead every day takes a toll both physically and mentally, and that makes it way more likely you’ll suffer from overtraining. Overtraining means you’re not giving your body enough time to recover, so the stress on your system builds up and can cause physiological changes including muscle damage and hormonal changes.

If you’re overtraining, your runs become less efficient (because you’re too tuckered out to give them your all) or may potentially stop altogether if you hurt yourself. Making time for slow running in between speed work allows you to keep training your aerobic system and increase its capacity (endurance) without pushing too far.

You shouldn’t be doing more than two high-intensity runs each week, Milton says. “If you’re doing them more frequently, the body doesn’t have enough time to recover, and they can wear you down more than increase performance and progress,” she explains.

Bottini adds that for some people, one good, hard speed run per week may be sufficient. “Sometimes that’s all that you need,” she says. You may feel like you’re not doing as much or working as hard, but she reassures that the work you’re doing is necessary. “You’re on your feet, going through the running motion, and simply getting your body used to being on the road or trail.” Eventually, if you’ve been building this base slowly, getting faster will feel easier.

Bottom line: No matter how crazy your life is and how much you have to modify a training schedule, make time to do those long runs and to do them slowly. Skimping on that foundational part of running because you want to do what seems quicker will just slow you down in the end.